1. Field of the Invention
The present invention relates to a mirror arrangement for use in a single lens reflex camera, and more particularly relates to a mirror arrangement for use in a single lens reflex camera wherein the light transmitted through an objective lens is divided into reflected light directed to a viewfinder and transmitted light which is passed to a light receptor for detecting a focusing condition or the like.
2. Description of the Prior Art
In a mirror arrangement of the kind described above, it has been known to divide the light transmitted through the objective lens into two portions by means of a half-mirror with a semi-transparent film of a metal such as aluminum or silver. However, with such a half-mirror, the half-mirror itself absorbs some of the light, making the image in the viewfinder dark and preventing the light receptor from receiving light of sufficient intensity. A means of improving such defects has been proposed in Japanese patent Laid Open No. 119030/1978, which discloses a mirror arrangement including a total reflection mirror surface with a plurality of very small transmitting pinholes disposed at random thereon. This mirror arrangement divides the light transmitted through the objective lens into a first portion that is led to the viewfinder by reflection, and a second portion that is led to the light receptor by transmission therethrough. With this construction, there is substantially no light absorbed by the mirror arrangement. However, the light transmitted through the mirror arrangement is diffracted by the pinholes over a wide range, therefore, an image forming condition of the objective lens is not maintained by the light transmitted through the mirror arrangement. Accordingly, if the light receptor is constructed to detect the image forming condition of the objective lens for discriminating a focusing condition of the lens, for example, if the light receptor comprises a plurality of small light receiving cells arranged in a predetermined direction as disclosed in U.S. Pat. No. 4,185,191, it is difficult to detect the focusing condition of the objective lens.
Furthermore, in the above mirror arrangement, it is troublesome to inspect the product because the degree of randomness of the light transmitting pinholes disposed on the total reflection mirror surface must be inspected.